1. Field of the Invention
The present invention relates to a magnetic thin film. More specifically, the present invention relates to a soft magnetic thin film suitable for a magnetic sensor such as a magnetic impedance sensor, a magnetic circuit component such as a magnetic coil and an inductor, a magnetic recording head, and a magnetic reproducing head. The present invention also relates to a magnetic head using such a magnetic thin film.
2. Description of the Prior Art
Recently, a magnetic material having both excellent magnetic characteristics and a high saturation magnetic flux density in a high frequency band of several MHz to several GHz has been demanded in the field of a magnetic device using a soft magnetic material, such as a magnetic recording head, a magnetic impedance sensor, and a magnetic circuit component such as a microinductor. In such a high frequency band, it is known that the magnetic characteristics are deteriorated by a loss due to magnetic domain wall resonance, ferromagnetic resonance or the like. Conventionally, in order to prevent such deterioration, for example, the number of magnetic domain walls in a film plane is reduced in the case of a Co based amorphous material having a low Curie temperature. In order to raise ferromagnetic resonance frequency, a technique of generating a strong uniaxial anisotropy in a material by performing a heat treatment in a magnetic filed or forming a film in a magnetic field has been used (Senda et al. MAG-94-95, pp77-83). For Fe or FeCo based crystalline material having a high Curie temperature, a technique of generating a uniaxial anisotropic magnetic field by using an inverse magnetostriction effect in a film plane has been used, in addition to the above-mentioned technique.
It is known that the relative permeability .mu..sub.r ' and the ferromagnetic resonance f.sub.k of a magnetic substance satisfy the following equations: EQU .mu..sub.r '(0)=4.pi.Ms.multidot.H.sub.k (1) EQU f.sub.k =(.gamma./2.pi.)(4.pi.Ms.multidot.H.sub.k).sup.1/2 (2)
where 4.pi.Ms represents a saturation magnetization, H.sub.k represents a uniaxial anisotropic magnetic field, and .gamma. represents a gyro-magnetic constant.
As seen from Equation (2), for a high frequency band magnetic device, a high saturation magnetization or a high uniaxial anisotropic magnetic field is required. Generally, a Co based amorphous material has a low saturation magnetization of about 10 kG, so that a high uniaxial anisotropic magnetic field is required. However, as seen from Equation (1), a high uniaxial anisotropic magnetic field leads to a low relative permeability. Furthermore, such an amorphous material cannot provide sufficient magnetization for magnetic recording in a medium having a high coercive force.
On the other hand, Fe or FeCo based crystalline material having a high saturation magnetization has a high Curie temperature, so that a heat treatment in a magnetic field or formation of a film in a magnetic field cannot provide a sufficient uniaxial anisotropic magnetic field. Furthermore, it is difficult to control the magnitude of anisotropy.
Especially, in a magnetron sputtering method often used for forming a magnetic thin film, the magnetostatic leakage field from a target is not uniform, so that it is difficult to provide a suitable uniaxial anisotropy. Furthermore, the uniaxial anisotropy that can be provided by an inverse magnetostriction effect in proportion to a product of an internal stress and a saturation magnetostriction is restricted by a stress distribution depending on the shape of the film. Furthermore, a high saturation magnetostriction degrades the magnetic characteristics.
With the development of the miniaturization of a magnetic device in recent years, a magnetic material tends to be processed into more miniaturized patterns. For example, for a magnetic head such as an MIG head (Metal In Gap head) and a head for a hard disk, a magnetic thin film is processed into a rectangular parallelopiped with dimensions in the range of about several hundreds of nanometers to several micrometers. In such a shape, the shape anisotropy is relatively low, so that the magnetization not only rotates in a specific plane but also easily moves in other planes.
Especially, a so-called granular material has a high saturation magnetic flux density, but the film structure is three-dimensionally isotropic. Therefore, since the freedom degree in the direction of the rotation magnetization is large, it is difficult to control the plane for the rotation magnetization. Furthermore, it is difficult to provide the magnetic anisotropy in a micro region uniformly by using an external magnetic field.